1. Field of the Invention
This invention relates to a thin-film conductor. This invention also relates to a method of fabricating a thin-film conductor.
2. Description of the Prior Art
In 1988, Roth and collaborators discovered the compound which is now known as the "all-layer phase" or the "parent structure" of all copper-oxide superconductors (T. Siegrist, S. M. Zahurak, D. W. Murphy, and R. S. Roth: Nature, Vol. 334, No. 6179, pp. 231-232, 1988). It is based on the infinite stacking of CuO.sub.2 planes separated only by the alkaline earth atoms "A" in the stacking sequence CuO.sub.2 --A--CuO.sub.2 --A . . . . Specifically, they reported the growth of small single crystals of the composition Ca.sub.0.84 Sr.sub.0.16 CuO.sub.2, and the characterization thereof by single-crystal X-ray diffraction. The crystals are tetragonal with space group P4/mmm, and the structure contains planer [CuO.sub.2 ].sub..infin. layers separated by Ca and Sr atoms.
Takano and coworkers discovered in 1989 that the all-layer phase could be stabilized for large alkaline earths by synthesis under high applied pressures (M. Takano, T. Takeda, H. Okada, M. Miyamoto, and K. Kusaka: Physica C 159, 375-378, 1989). They found that SrCuO.sub.2 and even (Ba, Sr)CuO.sub.2 solid solutions could be synthesized. Specifically, they reported the crystals of SrCuO.sub.2, Sr.sub.2/3 Ca.sub.1/3 CuO.sub.2, Sr.sub.1/2 Ca.sub.1/2 CuO.sub.2, and Sr.sub.1/3 Ca.sub.2/3 CuO.sub.2. Owing to the larger sizes of these alkaline earths, the lengths of the Cu-O bonds in the new materials were significantly larger than those in Ca.sub.0.84 Sr.sub.0.16 CuO.sub.2.
Takano and coworkers reported the composition dependence of the lattice constants and the bond lengths of ACuO.sub.2 upon the "A" cation radius where "A" denotes the alkaline earth atoms such as Sr, Sr.sub.1/2 Ca.sub.1/2, or Ca (M. Takano, M. Azuma, Z. Hiroi, and Y. Bando: Physica C 176, 441-444, 1991).
Azuma and coworkers reported the infinite-layer compound (Ca.sub.1-x Sr.sub.x).sub.1-y CuO.sub.2 where 0.4.ltoreq.x.ltoreq.0.7 and 0.ltoreq.y.ltoreq.0.1 (M. Azuma, Z. Hiroi, M. Takano, Y. Bando, and Y. Takeda: Nature, Vol. 356, pp. 775-776, April 1992). They also reported the compound (Ca.sub.0.3 Sr.sub.0.7).sub.0.9 CuO.sub.2-.delta. where .delta.&gt;0.
It is known to make the composition ACuO.sub.2 such as Ca.sub.0.84 Sr.sub.0.16 CuO.sub.2 by sintering under high pressures. Powders of the composition of ACuO.sub.2 are available through the sintering process. A thin film of the composition of ACuO.sub.2 is unavailable. In some cases, thin-film conductors are suitable for use in various electric devices.